Semiconductor light emitting devices having an uneven emission pattern layer and methods of manufacturing the same

ABSTRACT

Example embodiments are directed to light-emitting devices (LEDs) and methods of manufacturing the same. The LED includes a first semiconductor layer; a second semiconductor layer; an active layer formed between the first and second semiconductor layers; and an emission pattern layer including a plurality of layers on the first semiconductor layer, the emission pattern including an emission pattern for externally emitting light generated from the active layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/929,149, filed Jan. 4, 2011, and claims priority under 35 U.S.C.§119 to Korean Patent Application No. 10-2010-0071976, filed on Jul. 26,2010, in the Korean Intellectual Property Office, the disclosure of eachof which is incorporated herein in their entirety by reference.

BACKGROUND

1. Field

Example embodiments relate to light-emitting devices (LEDs) and methodsof manufacturing the same.

2. Description of the Related Art

Semiconductor light-emitting devices (LEDs) are highly efficient andenvironment-friendly light sources that are used in various devices suchas displays, optical communication devices, vehicles, and/or generallamps. Currently, as a result of the development of white light LEDs,LED technology is also found in general purpose lamps. A white light LEDmay be formed by combining, for example, a blue or ultraviolet LED and aphosphor, or combining red, green, and blue LEDs.

A blue or ultraviolet LED that is a main component of a white light LEDis formed by using a gallium nitride (GaN)-based compound semiconductor.A GaN-based compound semiconductor has a wide bandgap and may emit lightof almost all wavelengths from ultraviolet light to visual light,according to the composition of a nitride.

Typically, a thin film-type GaN LED is formed by growing a GaN thin filmon a sapphire (Al₂O₃) substrate. However, if a GaN-based compoundsemiconductor is grown on a sapphire substrate in the form of a thinfilm, light emitting efficiency is reduced due to a mismatch in latticeconstant or a difference in thermal expansion coefficient, and largearea growth is difficult, and thus manufacturing costs may increase.Also, when a laser lift-off (LLO) process is performed to remove asapphire substrate after growing a GaN thin film, the output of lightmay be reduced due to laser impact.

In order to increase a manufacturing yield and reduce manufacturingcosts of LEDs, a method of manufacturing a GaN LED using a siliconsubstrate is currently suggested. A silicon substrate having a wafer ofa diameter greater than 12 inches may exhibit less warping in a hightemperature process as compared to a sapphire substrate. Also, if asilicon substrate is used, after growing a GaN thin film, the siliconsubstrate may be removed without performing an LLO process and thus theoutput of light may not be reduced.

SUMMARY

According to example embodiments, a light-emitting device (LED) includesa first semiconductor layer of a first impurity type; a secondsemiconductor layer of a second impurity type; an active layer betweenthe first and second semiconductor layers; and an emission pattern layeron the first semiconductor layer, the emission pattern layer including aplurality of layers and having an emission pattern that externally emitslight generated from the active layer.

According to example embodiments, the emission pattern layer comprisesan aluminum nitride (AlN) layer and an aluminum gallium nitride (AlGaN)layer.

According to example embodiments, the emission pattern layer comprisesan AlN layer, and AlGaN layers and gallium nitride (GaN) layersalternately formed on the AlN layer.

According to example embodiments, the LED, further includes a metallayer under the second semiconductor layer and configured to reflectlight generated from the active layer toward the emission pattern layer.

According to example embodiments, the LED, further includes aninsulating layer between the metal layer and the second semiconductorlayer.

According to example embodiments, the LED, further includes a firstcontact layer that penetrates the insulating layer, the secondsemiconductor layer, and the active layer, and contacts the firstsemiconductor layer and the metal layer.

According to example embodiments, the LED, further includes a secondcontact layer on a portion between the insulating layer and the secondsemiconductor layer, the second contact layer penetrating the secondsemiconductor layer, the active layer, and the first semiconductorlayer.

According to example embodiments, the LED, further includes a GaN layerbetween the first semiconductor layer and the emission pattern layer.

According to example embodiments, the emission pattern is uneven.

According to example embodiments, a depth of the uneven emission patternis from about 500 nm to about 1500 nm.

According to example embodiments, a method of manufacturing alight-emitting device (LED) includes forming a buffer layer on a firstsubstrate; sequentially forming a first semiconductor layer of a firstimpurity type, an active layer, and a second semiconductor layer of thesecond impurity type on the buffer layer; forming a first contact layercontacting the first semiconductor layer, and a second contact layercontacting the second semiconductor layer; and forming an emissionpattern layer by removing the first substrate and patterning the bufferlayer.

According to example embodiments, the forming of the first and secondcontact layers includes forming a first through hole penetrating throughthe second semiconductor layer and the active layer to expose a portionof the first semiconductor layer; forming an insulating layer on asurface of the second semiconductor layer and a sidewall of the firstthrough hole; forming the first contact layer by filling the firstthrough hole with metal; and forming the second contact layer by usingmetal on a portion of the second semiconductor layer, the secondsemiconductor layer being exposed by etching a portion of the insulatinglayer on the second semiconductor layer, and covering the second contactlayer with an insulator.

According to example embodiments, the method, further includes forming ametal layer on the insulating layer and the first contact layer.

According to example embodiments, the method, further includes bonding asecond substrate on the metal layer and removing the first substrate.

According to example embodiments, the method, further includes forming asecond through hole penetrating through the emission pattern layer, thefirst semiconductor layer, the active layer, and the secondsemiconductor layer to expose the second contact layer; and filling thesecond through hole with metal to contact the second contact layer.

According to example embodiments, the method, further includes removingthe first substrate using a lapping process or an etching process.

According to example embodiments, the buffer layer includes an aluminumnitride (AlN) layer and an aluminum gallium nitride (AlGaN) layer.

According to example embodiments, the buffer layer includes an AlNlayer, and AlGaN layers and gallium nitride (GaN) layers alternatelyformed on the AlN layer.

According to example embodiments, the method, further includes formingan uneven emission pattern layer on the buffer layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent bydescribing in detail example embodiments with reference to the attacheddrawings. The accompanying drawings are intended to depict exampleembodiments and should not be interpreted to limit the intended scope ofthe claims. The accompanying drawings are not to be considered as drawnto scale unless explicitly noted.

FIG. 1 is a cross-sectional view of a light-emitting device (LED)according to example embodiments;

FIG. 2 is a cross-sectional view of an LED according to exampleembodiments; and

FIGS. 3A through 3L are cross-sectional views for describing a method ofmanufacturing an LED, according to example embodiments.

DETAILED DESCRIPTION

Detailed example embodiments are disclosed herein. However, specificstructural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments. Exampleembodiments may, however, be embodied in many alternate forms and shouldnot be construed as limited to only the embodiments set forth herein.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the drawings and will herein be described in detail.It should be understood, however, that there is no intent to limitexample embodiments to the particular forms disclosed, but to thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of exampleembodiments. Like numbers refer to like elements throughout thedescription of the figures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it may be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between”, “adjacent” versus “directlyadjacent”, etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising,”, “includes” and/or “including”, when usedherein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

FIG. 1 is a cross-sectional view of a light-emitting device (LED) 100according to example embodiments. Referring to FIG. 1, the LED 100includes first type and second type semiconductor layers 160 and 140formed on a substrate 110, an active layer 150 formed between the firsttype and second type semiconductor layers 160 and 140, and an emissionpattern layer 180 on the first type semiconductor layer 160, including aplurality of layers, and having an emission pattern for externallyemitting light generated from the active layer 150.

A metal layer 120 that reflects light generated from the active layer150 in the direction of the substrate 110 such that the light isexternally emitted through the emission pattern layer 180 may be underthe second type semiconductor layer 140.

An insulating layer 130 may be formed between the metal layer 120 andthe second type semiconductor layer 140. The insulating layer 130insulates a first contact layer (not shown) contacting and applies avoltage to the first type semiconductor layer 160, from a second contactlayer (not shown) contacting and for applying a voltage to the secondtype semiconductor layer 140. Detailed structures of the first andsecond contact layers will be described later with reference to FIG. 3A.

A gallium nitride (GaN) layer 170 may be further prepared between thefirst type semiconductor layer 160 and the emission pattern layer 180.The GaN layer 170 is not doped with impurities and may be formed as apart of a buffer layer.

The first type semiconductor layer 160 may be formed of a nitridesemiconductor doped with an n-type impurity, e.g., n-Al_(x)Ga_(y)In_(z)N(x+y+z=1). The second type semiconductor layer 140 may be formed of anitride semiconductor doped with a p-type impurity, e.g.,p-Al_(x)Ga_(y)In_(z)N (x+y+z=1). The active layer 150 may include singleor multiple quantum wells obtained by varying x, y, and z values inAl_(x)Ga_(y)In_(z)N to adjust a bandgap. A light emission wavelengthvaries according to a mole fraction of indium (In) in indium galliumnitride (InGaN) used in forming the active layer 150. For example, asthe content of In increases, a color of emitted light changes to a longwavelength band.

The emission pattern layer 180 is such that a majority of lightgenerated from the active layer 150 is externally emitted from the LED100. The emission pattern layer 180 may include an aluminum galliumnitride (AlGaN) layer 181 and an aluminum nitride (AlN) layer 189. Aswill be described later, the AlN layer 189 and the AlGaN layer 181 areformed as a buffer layer for growing nitride thin films on aheterogeneous substrate. In example embodiments, the emission pattern isformed by texturing a surface of the buffer layer. The AlN layer 189 andthe AlGaN layer 181 may be etched to have an uneven pattern havingV-shaped recesses, for example.

The depth of the uneven pattern may be from about 500 nm to about 1500nm. Although the depth of the uneven pattern is the same as the sum ofthe thicknesses of the AlN layer 189 and the AlGaN layer 181 in FIG. 1,example embodiments are not limited thereto and the depth of the unevenpattern may vary to a desired depth in the AlGaN layer 181 or the GaNlayer 170.

Although the emission pattern layer 180 has the uneven pattern formed byetching the AlGaN layer 181 and the AlN layer 189 in FIG. 1, exampleembodiments are not limited thereto and the emission pattern layer 180may have the uneven pattern formed by performing a surface texturingprocess to a predetermined/desired depth into the GaN layer 170.

FIG. 2 is a cross-sectional view of an LED 200 according to exampleembodiments. FIG. 2 is different from FIG. 1 in layers included in theemission pattern layer 180. The emission pattern layer 180 of thepresent embodiment includes the AlN layer 189, and AlGaN layers 185 andGaN layers 183 alternately formed below the AlN layer 189. Although twoAlGaN layers 185 and two GaN layers 183 are alternately formed in FIG.2, example embodiments are not limited thereto.

FIGS. 3A through 3L are cross-sectional views describing a method ofmanufacturing an LED 300, according to example embodiments.

Referring to FIG. 3A, initially, an AlN layer 389, an AlGaN layer 381, aGaN layer 370, a first type semiconductor layer 360, an active layer350, and a second type semiconductor layer 340 are sequentially formedon a first substrate S.

The first substrate S may be, for example, a silicon substrate, Si(111).

The AlN layer 389 and the AlGaN layer 381 are formed as a buffer layerfor growing nitride thin films. AlN for forming the AlN layer 389 is acompound semiconductor in a wurtzite crystal having partial ionicbonding characteristics of aluminum (Al) and nitrogen (N) atoms andhaving a covalent bond hexagonal structure, has the largest energybandgap from among Group III-V semiconductors, and has crystallinestructural anisotropy and a stoichiometric bonding structure. Also, AlNhas high elasticity, high heat conductivity, thermal stability,excellent transmittance and high refractive index in a range from visuallight to infrared light, and stability at room-temperature atmosphericpressure. AlN may be used together with AlGaN as a buffer layer forgrowing high-quality nitride thin films having relatively fordislocation or cracks. The thickness of the buffer layer may be fromabout 200 nm to about 3 um and may be determined to suppress theoccurrence of dislocation or cracks when growing the nitride thin filmsand to ensure a desired crack-free thickness. The buffer layer is notlimited to the structure illustrated in FIG. 3A and may have a structurein which AlGaN layers and GaN layers are alternately formed on the AlNlayer 389.

The GaN layer 370 may be further formed on the AlGaN layer 381. The GaNlayer 370 may be an undoped-GaN (u-GaN) layer, for example

The first type semiconductor layer 360 may be formed of a nitridesemiconductor doped with an n-type impurity, e.g., n-Al_(x)Ga_(y)In_(z)N(x+y+z=1). The active layer 350 may include single or multiple quantumwells obtained by varying x, y, and z values in Al_(x)Ga_(y)In_(z)N toadjust a bandgap. The second type semiconductor layer 340 may be formedof a nitride semiconductor doped with a p-type impurity, e.g.,p-Al_(x)Ga_(y)In_(z)N (x+y+z=1).

The above-described nitride thin films may be formed by performing asemiconductor manufacturing process such as a metal organic chemicalvapor deposition (MOCVD) process, for example.

Referring to FIG. 3B, a through hole h1 is formed to penetrate throughthe second type semiconductor layer 340 and the active layer 350 and toexpose a region of the first type semiconductor layer 360. The throughhole h1 is prepared to form a first contact layer (not shown) contactingand for applying a voltage to the first type semiconductor layer 360.Initially, a photoresist layer pr is coated on the second typesemiconductor layer 340 and then is patterned into apredetermined/desired pattern. The second type semiconductor layer 340,the active layer 350, and the first type semiconductor layer 360 areetched by using the photoresist layer pr as a mask, to form the throughhole h1. The through hole h1 may be formed by performing a dry etchingprocess, for example.

Referring to FIG. 3C, an insulating layer 330 is formed on a surface ofthe second type semiconductor layer 340 and a sidewall of the throughhole h1. The insulating layer 330 may be formed of, for example, SiO₂.

Referring to FIG. 3D, a first contact layer m1 that contacts the firsttype semiconductor layer 360 is formed by filling the through hole h1with metal. The first contact layer m1 may be formed by depositing, forexample, titanium/aluminum/titanium/platinum (Ti/Al/Ti/Pt).

Referring to FIG. 3E, an insulating material is further coated to coverthe first contact layer m1 and the insulating layer 330, and a portionof the insulating layer 330 on the second type semiconductor layer 340is etched to expose a region of the second type semiconductor layer 340.

Referring to FIG. 3F, a second contact layer m2 is formed by filling theexposed portion with metal. The second contact layer m2 may be formed bydepositing, e.g., nickel/silver/titanium/platinum (Ni/Ag/Ti/Pt).

Referring to FIG. 3G, a metal layer 320 is formed on the insulatinglayer 330. In this case, an insulating material is further coated on theinsulating layer 330 on the second contact layer m2 such that the metallayer 320 is insulated from the second contact layer m2, and a portionof the insulating layer 330 on the first contact layer m1 is removedsuch that the metal layer 320 contacts the first contact layer m1. Themetal layer 320 may be formed by depositing, for example,titanium/gold/tin/gold/tin/gold (Ti/Au/Sn/Au/Sn/Au).

Referring to FIG. 3H, a second substrate 310 is bonded onto the metallayer 320. The second substrate 310 may be, for example, a siliconsubstrate, Si(100). The second substrate 310 may be bonded on the metallayer 320 by using a eutectic bonding method, for example.

Referring to FIG. 3I, the first substrate S is removed. For example, agrinding or lapping process may be performed to reduce the thickness ofthe first substrate S, and then a dry or wet etching process may beperformed. The lapping process and the etching process are performedtogether in order to reduce etching damages in nitride thin films, ormay be performed individually one after the other. Also, since the firstsubstrate S formed of silicon substrate is removed as described above,light extraction efficiency may be increased in comparison to a casewhen a sapphire substrate is used. If nitride thin films are formed on asapphire substrate and then the sapphire substrate is removed byperforming a laser lift-off (LLO) process, the output of light may bereduced due to laser impact.

Referring to FIG. 3J, a surface texturing process is performed. The AlNlayer 389 and the AlGaN layer 381 are patterned into apredetermined/desired pattern to form the emission pattern layer 380.The emission pattern layer 380 may have an uneven pattern havingV-shaped recesses as illustrated in FIG. 3J, but is not limited thereto.Although the uneven pattern is formed by etching the AlN layer 389 andthe AlGaN layer 381 in FIG. 3J, the uneven pattern may be formed byperforming etching to a predetermined/desired depth in the AlGaN layer381 or the GaN layer 370. The depth of the uneven pattern may be fromabout 500 nm to about 1500 nm. In the above-described surface texturingprocess, a wet etching process using potassium hydroxide (KOH) may beperformed, for example. Since the wet etching process allowssimultaneous etching of a plurality of layers in a short time, processcost and time are reduced. The uneven pattern having a depth of about400 nm may be formed in about 5 to 10 minutes. The size of or thedistance between unit pieces of the uneven pattern may be varied toincrease light extraction efficiency. For example, the uneven patternmay be set to form multiple scattering points and to have a uniformsize.

Referring to FIG. 3K, a through hole h2 is formed to penetrate throughthe emission pattern layer 380, the GaN layer 370, the first typesemiconductor layer 360, the active layer 350, and the second typesemiconductor layer 340 and to expose a region of the second contactlayer m2. Like the through hole h1 formed in FIG. 3B, the through holeh2 may be formed by performing a photolithography process and an etchingprocess, for example. Also, an insulating layer 333 is coated on asidewall of the through hole h2.

Referring to FIG. 3L, an electrode unit 390 is formed by depositingmetal on the second contact layer m2 through the through hole h2. Theelectrode unit 390 may be formed by depositing, for example, Ti/Au.Although not shown in FIG. 3L, an electrode unit for applying a voltageto the first type semiconductor layer 360 through the metal layer 320and the first contact layer m1 may be further formed on a lower surfaceof the second substrate 310.

In example embodiments, the first contact layer m1 and the secondcontact layer m2 are exemplarily formed to apply a voltage to the firsttype semiconductor layer 360 and the second type semiconductor layer340, and their structures and/or forming processes may be varied.

As such, the LED 300 capable of reducing process cost and time andincreasing light extraction efficiency is manufactured.

As described above, according to example embodiments, since MN and AlGaNfor forming an emission pattern layer and nitride semiconductors forforming a light emitting structure are similar materials, the emissionpattern layer and the light emitting structure have almost the samerefractive index very little amount of light may be reflected at theboundaries between layers of an LED. Also, total reflection at aboundary to the external of the LED may be reduced due to a texturedsurface. Accordingly, light extraction efficiency of the LED may beincreased.

In addition, process cost and time for manufacturing the LED may bereduced.

Example embodiments having thus been described, it will be obvious thatthe same may be varied in many ways. Such variations are not to beregarded as a departure from the intended spirit and scope of exampleembodiments, and all such modifications as would be obvious to oneskilled in the art are intended to be included within the scope of thefollowing claims.

What is claimed is:
 1. A method of manufacturing a light-emitting device(LED), the method comprising: forming a buffer layer on a firstsubstrate; sequentially forming a first semiconductor layer of a firstimpurity type, an active layer, and a second semiconductor layer of asecond impurity type on the buffer layer; forming a first contact layercontacting the first semiconductor layer, and a second contact layercontacting the second semiconductor layer; and forming an emissionpattern layer by removing the first substrate and patterning the bufferlayer, wherein the forming of the first and second contact layerscomprises, forming a first through hole penetrating through the secondsemiconductor layer and the active layer to expose a portion of thefirst semiconductor layer, forming an insulating layer on a surface ofthe second semiconductor layer and a sidewall of the first through hole,forming the first contact layer by filling the first through hole withmetal, and forming the second contact layer by using metal on a portionof the second semiconductor layer, the second semiconductor layer beingexposed by etching a portion of the insulating layer on the secondsemiconductor layer, and covering the second contact layer with aninsulator.
 2. The method of claim 1, further comprising forming a metallayer on the insulating layer and the first contact layer.
 3. The methodof claim 2, further comprising bonding a second substrate on the metallayer and removing the first substrate.
 4. The method of claim 3,further comprising: forming a second through hole penetrating throughthe emission pattern layer, the first semiconductor layer, the activelayer, and the second semiconductor layer to expose the second contactlayer; and filling the second through hole with metal to contact thesecond contact layer.
 5. The method of claim 1, further comprisingremoving the first substrate using a lapping process or an etchingprocess.
 6. The method of claim 1, wherein the buffer layer comprises analuminum nitride (AlN) layer and an aluminum gallium nitride (AlGaN)layer.
 7. The method of claim 1, wherein the buffer layer comprises anAlN layer, and AlGaN layers and gallium nitride (GaN) layers alternatelyformed on the AlN layer.
 8. The method of claim 1, wherein the formingthe emission pattern layer forms an uneven emission pattern layer on thebuffer layer.